Generally, a wireless communication system uses a predetermined RF band for transmitting/receiving data. For example, in IEEE802.11g known as an American standard of a local area network (LAN), the RF band of 2.4 GHz to 2.47 GHz is used and 54 Mbps is achieved as the maximum data rate in the range of the communication distance of 50 m to 100 m.
However, demands for data of general users are increasing year by year. It is strongly desired to download not only high definition image data but also music data and movie data to portable equipment of the user in short time.
One of techniques addressing the demand is ultra wide band (UWB) wireless communication. Since Federal Communications Commission has permitted commercial use of UWB in April 2002, many organizations have been conducting research and development on the technique. The technique employs a multiband configuration that the frequency range used for the UWB wireless communication is divided into a plurality of frequency bands. In the case of transmitting/receiving data using the multiband, in a frequency band of a signal obtained by modulating/demodulating data, it is necessary to transmit the signal without attenuation as much as possible or necessary to amplify the signal. In the frequency band in which data is not transmitted, it is necessary to attenuate an unwanted signal existing in the band in order to prevent cross modulation.
According to non-patent document 1, a frequency synthesizer for a multiband (MB) OFDM (Orthogonal Frequency Division Multiplexing) system needs band-switching time in the order of nanoseconds and has a difficult challenge on unwanted sideband spectrum and power consumption. Typically, a general PLL-based frequency synthesizer is not simply suitable due to its long settling time of microseconds. The non-patent document 1 describes a high-speed-hopping frequency synthesizer for generating clocks in seven bands distributing from 3 GHz to 8 GHz in switching time of 1 nanosecond. The frequency synthesizer is comprised of two PLL (Phase Locked Loop) circuits, two selectors, and one SSB (Single Side Band) mixer.
Non-patent document 2 describes a gyrator. The gyrator has two transconductance circuits gm1 and gm2 whose input and output terminals are connected in a closed loop configuration, a capacitor C1 connected to the output terminal of the transconductance circuit gm1 and the input terminal of the transconductance circuit gm2, and a capacitor C2 and a resistor R connected to the output terminal of the transconductance circuit gm2 and the input terminal of the transconductance circuit gm1. The gyrator makes the capacitor C2 behave as an inductor L of C2/(gm1·gm2). As described above, the gyrator sets the input impedance as the inverse number of the impedance connected to the output, and can transform a capacitor equivalently to an inductor. Therefore, when a circuit is configured like an LC circuit by using the equivalently transformed inductor, a filter and a resonant circuit can be formed without using an inductor which is difficult to be integrated.
Non-patent document 3 describes a biquad bandpass filter similar to the gyrator described in the non-patent document 2. The non-patent document 3 describes a CMOS full-differential biquad lattice bandpass filter capable of tuning performance index Q and center frequency of the filter with bias voltage and bias current. By adjusting the bias current to 380 μA to 800 μA, the center frequency can be tuned to 2.45 GHz to 2.85 GHz by constant gain and bandwidth.
Non-patent document 4 describes a technique of using a combination of a gyrator and a capacitor for emulating the inductor for an RF low-noise amplifier of 900 MHz frequency band in order to avoid using an external inductor and on-chip spiral inductor which are expensive. The gyrator is comprised of two transconductance circuits (gm1 and gm2) which are connected in a negative feedback form. A first capacitance (C1) as a capacitive load configured by a device parasitic capacitor between the circuits generates an input inductance impedance L. The first capacitance (C1) and a second capacitance (C2) on the input side form an LC tank circuit. The LC tank circuit operates as a load on the input-side transconductance circuit. The center frequency of the LC tank circuit is given by ½π(C1C2/gm1gm2)1/2.
In the RF low noise amplifier, a differential RF signal is supplied to the source of each of a pair of grounded-gate NMOS transistors as the input-side transconductance circuit. To the drains of the pair of grounded-gate NMOS transistors, the gates of a differential pair of NMOS transistors as the transconductance circuit in the first stage of the gyrator are connected. To the drains of the differential pair of NMOS transistors, a pair of PMOS current-mirror-type loads are connected, and the gates of a pair of PMOS transistors as the transconductance circuit in the second stage of the gyrator are also connected. By connecting the gates of the differential pair of NMOS transistors as the transconductance circuit of the first stage of the gyrator to the drains of the pair of PMOS transistors as the transconductance circuit of the second stage of the gyrator, negative feedback is realized.
The frequency characteristics of the CMOS low-noise amplifier configured as described above are also measured. It is also reported that the amplifier has a gain of about 20 dB around the center frequency of 0.9 GHz and also a gain of about 10 dB around a lower frequency of 0.4 GHz and a higher frequency of 1.4 GHz.    [Non-patent document 1] Jri Lee et al, “A 7-Band 3-8 GHz Frequency Synthesizer with 1 ns Band-Switching Time in 0.18 μm CMOS Technology”, IEEE Solid-State Circuits Conference DIGEST OF TECHNICAL PAPERS, pp. 204 to 205    [Non-patent document 2] A. A. Abidi, “Noise in Active Resonators and the Available Dynamic Range”, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS-I: FUNDAMENTAL THEORY AND APPLICATIONS, VOL. 39, NO. 4, APRIL 1992, pp. 296 to 299    [Non-patent document 3] Apinunt Thanachayanont, “LOW VOLTAGE LOW POWER CMOS INDUCTORLESS RF BANDPASS FILTER WITH HIGH IMAGE REJECTION CAPABILITY”, The 2002 45th Midwest Symposium on Circuits and Systems, Volume 3, pp III-548 to 551    [Non-patent document 4] Young J. Shin et al, “An Inductorless 900 MHz, RF Low-Noise Amplifier in 0.9 μm CMOS”, IEEE 1997 CUSTOM INTEGRATED CIRCUITS CONFERENCE, PP. 513 to 516